The present disclosure relates to an image forming apparatus, and an abnormality detection apparatus and an abnormality detection method for a humidity sensor device.
An image forming apparatus such as a printer, a copying machine or a multifunction peripheral may be provided with a humidity sensor. For example, the humidity sensor is used for detecting humidity in order to keep the quality of image formation constant by controlling the charge amount of a photoconductive drum or the like in accordance with the change of ambient humidity. The humidity sensor may be, however, damaged by deterioration over time or the like. Therefore, a method or an apparatus for detecting a malfunction of the humidity sensor has been proposed.
For example, an image forming apparatus including a humidity sensor element, a resistor, a signal output section and a measurement section has been proposed. In an example of such an image forming apparatus, the resistance value of the humidity sensor element is varied in accordance with humidity change. The resistor is serially connected to the humidity sensor element. The signal output section outputs a clock signal (for example, with a frequency of 1 kHz and a pulse time width of 500 μs) to the humidity sensor element and the resistor. The measurement section detects a voltage on a node between the humidity sensor element and the resistor at a timing precedently determined based on a rising edge or a falling edge of the clock signal (for example, 250 μs after a rising or falling edge), and obtains a humidity on the basis of the value of the detected voltage. In accordance with the detected voltage, the measurement section detects a voltage at a timing different from the precedently determined timing (for example, 50 μs after a rising or falling edge). Thus, abnormality of the humidity sensor element can be detected.
Alternatively, a humidity sensor controller for detecting deterioration of a humidity sensor by comparing a sensor output of the humidity sensor with a sensor output of a normal humidity sensor has been disclosed. Besides, an air conditioner for a vehicle that detects a malfunction caused by characteristic deterioration of a humidity sensor depending upon whether or not a humidity detection signal is varied in a state where the humidity in the vehicle is varied (as, for example, immediately after starting a dehumidifying operation) has been disclosed.